The human large intestine is colonised with a wide range of bacteria that have both positive and negative effects on gut physiology as well as having other systemic influences. Predominant groups of bacteria found in the colon include bacteroides, bifidobacteria, eubacteria, clostridia and lactobacilli. The bacteria present have fluctuating activities in response to substrate availability, redox potential, pH, O2 tension and distribution in the colon. In general intestinal bacteria can be divided into species that exert either potentially harmful or beneficial effects on the host. Pathogenic effects (which may be caused by clostridia or bacteroides, for example) include diarrhoea, infections, liver damage, carcinogenesis and intestinal putrefaction. Health-promoting effects may be caused by the inhibition of growth of harmful bacteria, stimulation of immune functions, improving digestion and absorption of essential nutrients and synthesis of vitamins. An increase in numbers and activities of bacterial groups (such as bifidobacteria and lactobacilli) that may have health promoting properties is desirable.
As far as infants specifically are concerned, immediately before birth, the gastrointestinal tract of a baby is thought to be sterile. During the process of birth, it encounters bacteria from the digestive tract and skin of the mother and starts to become colonised. Large differences exist with respect to the composition of the gut microbiota in response to the infant's feeding. The decal flora of breast-fed infants includes appreciable populations of bifidobacteria with some Lactobacillus species, whereas formula-fed infants have more complex microbiota, with bifidobacteria, bacteroides, clostridia and streptococci all usually present. After weaning, a pattern of gut microbiota that resembles the adult pattern becomes established.
Mother's milk is recommended for all infants. However, in some cases breast feeding is inadequate or unsuccessful for medical reasons or the mother chooses not to breast feed. Infant formulas have been developed for these situations.
One approach to promote the numbers and/or activities of beneficial bacteria in the colon is the addition of prebiotics to foodstuffs. A prebiotic is a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health. Such ingredients are non-digestible in the sense that they are not broken down and absorbed in the stomach or small intestine and thus pass intact to the colon where they are selectively fermented by the beneficial bacteria. Examples of prebiotics include certain oligosaccharides, such as fructooligosaccharides (FOS) and galactooligosaccharides (GOS).
Human milk is known to contain a larger amount of indigestible oligosaccharides than most other animal milks. In fact, indigestible oligosaccharides represent the third largest solid component (after lactose and lipids) in breast milk, occurring at a concentration of 12-15 g/l in colostrum and 5-8 g/l in mature milk. Human milk oligosaccharides are very resistant to enrymatic hydrolysis, indicating that these oligosaccharides may display essential functions not directly related to their calorific value.
As the composition of human milk becomes better understood, it has also been proposed to add prebiotics to infant formula. Various infant formulas supplemented with prebiotics such as mixtures of fructooligosaccharides and galactooligosaccharides for example are commercially available. However, such mixtures approximate only roughly the mixture of oligosaccharides in human milk. Over 100 different oligosaccharide components have been detected in human milk some of which have not been so far detected in animal milks such as bovine milk at all or have been detected only in small quantities. Examples of classes of human milk oligosaccharide that are present in bovine milk and colostrum only in very small quantities or not at all are sialylated and fucosylated oligosaccharides.
U.S. Patent Application No. 2003/0129278 describes an oligosaccharide mixture based on oligosaccharides produced from one or several animal milks which is characterized in that it comprises at least two oligosaccharide fractions which are each composed of at least two different oligosaccharides, with free lactose not pertaining thereto. The total spectrum of the oligosaccharides present in the oligosaccharide mixture differs from those present in the animal milk or animal milks from which the oligosaccharide fractions were extracted. Further a) if said oligosaccharides are extracted from only one animal milk the proportion of neutral oligosaccharides to acidic (sialylated) oligosaccharides is 90-60: 10-40 weight %, or b) if said oligosaccharides are extracted from at least two animal milks, the oligosaccharides extracted from two different animal milks each make up 10 weight % of the total amount of oligosaccharides present in the oligosaccharide mixture.
U.S. Pat. No. 5,270,462 describes a process for recovering, from cheese whey or rennet whey, sialic acid-bound oligosaccharides, sialic acid-bound peptides and sialic acid-bound lipids at a high concentration, comprising the steps of adjusting cheese whey or rennet whey to a pH of 2-5; contacting the whey with a cation exchanger to produce an exchanger-passed solution; and concentrating and/or desalting said exchanger-passed solution. The resulting composition with a high content of sialic acids can be utilized as food materials or medical materials.
EP 0 458 358 relates to a process for producing skim milk powder containing 10-15% by weight of galacto-oligosaccharide, which comprises:
(i) concentrating skim milk to obtain concentrated milk with a solid content of 20-50% by weight,
(ii) adding β-galactosidase to the concentrated milk to give rise to an enzymatic reaction,
(iii) heating the resulting reaction mixture for 30 seconds to 15 minutes to a temperature of 70-85° C. in order to terminate the enzymatic reaction, and
(iv) spray-drying the reaction-terminated mixture.
An object of the invention is to provide an oligosaccharide mixture which is effective as a prebiotic, particularly in the human gut and which has an oligosaccharide profile closer to that of human milk than that provided by mixtures of fructo- and galacto-oligosaccharides.